Saturday, November 27, 2010

Shifting Diving Geometry in Whale Sharks

I read a very interesting paper in the British Ecological Society's journal Functional Ecology. The scientists describe how Whale sharks (Rhincodon typus)use geometry to enhance their natural negative buoyancy. The research at Ningaloo Reef in Western Australia was headed by Dr Adrian Gleiss from Swansea University.

The scientists attached animal-borne motion sensors and accelerometers, to the free-swimming Whale sharks to measure their swimming activity and vertical movement.

The data collected revealed that sharks are able to glide without investing energy into movement when descending, but they had to beat their tails when they ascended. This is because sharks, unlike many fish, have negative buoyancy. The steeper the sharks ascended, the harder they had to beat their tail.

The Whale sharks displayed two kinds of movement modes. One was shallow ascent angles, which minimize the energetic demands of moving in the horizontal while the second movement of steeper ascent angles, optimized the energetic cost of vertical movement. The scientists conclude that geometry plays a crucial role in movement strategies of sharks. Movement geometry significantly affects power requirements in a manner similar to travel speed. Sharks are presumed to shift diving geometry with changing currencies and ecological context.